Treatment of iron contaminated liquids with an activated iron solids (AIS) process

ABSTRACT

The present invention is a method and system for treating iron-contaminated water (e.g., mine drainage) using an innovative treatment approach identified herein as the Activated Iron Solids (AIS) Process. The AIS process is capable of oxidizing and removing iron as iron oxides from iron-contaminated waters (such as, mining-related discharge, groundwater, surface water and industrial waste streams) producing a clean effluent. The AIS process is performed in a single or multiple tank system in which a catalytic surface chemistry process increases the iron removal 1000s times faster than would naturally occur and 100s of times faster than existing arts (e.g., aerobic pond passive treatment). In addition, the AIS process can utilize inexpensive alkaline material (such as, pulverized limestone) where initial mine drainage alkalinity (mg/L as CaCO 3 ) to ferrous iron (mg/L) ratio is less than approximately 1.7. Excess accumulated iron oxides are periodically removed from the systems using a waste activated iron solids (WAIS) system and is directed to an Iron Oxide Thickener where the iron oxides are further concentrated.

RELATED APPLICATION

This patent application is a continuation in part to a pending patentapplication, entitled, “A process and System for Treating IronContaminated Liquids” filed Jun. 3, 2003, Ser. No. 10/453,127, whichclaims priority from a provisional patent application entitled, “AProcess and Device for Treating Iron Contaminated Liquids” filed Jun. 3,2002, Ser. No. 60/384,680.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a device and method for and thetreatment of iron-contaminated fluid (e.g., mining-related discharge,groundwater, surface water and industrial waste streams) and, moreparticularly, to an apparatus and method for oxidizing and removingferrous iron from iron-contaminated fluid, including mine drainage, andproducing an effluent substantially free of iron.

2. Description of the Prior Art

Iron-contaminated water result from a variety of natural andanthropogenic processes with the later typically involving mining andindustrial processing. Ferrous iron is released from minerals (e.g.,pyrite, siderite, and hematite) through dissolution and redox processes.Industrial processing typically involves formation of reduced iron (Fe⁰)into various metallic compounds, with waste streams or subsequentoxidation causing elevated ferrous iron levels.

The most common source of iron-contaminated water results from mineralextraction and can be produced from either surface or deep miningpractices where iron sulfide minerals contained in the minerals andsurrounding formations are oxidized. The chemistry of mine drainage willvary depending on overburden characteristics and mining and reclamationtechniques. In the United States millions of gallons of mine drainage isproduced daily from both active and abandoned mine sites. Treating minedrainage is an expensive endeavor involving land, construction,materials, operation, maintenance and chemical costs. Left untreated,mine drainage contaminants surface and groundwater causing impacts totheir social, recreational and commercial uses.

Iron is removed from iron-contaminated waters employing chemical andpassive treatment technologies. Current chemical treatment, morecommonly used for industrial sources and active mines, requirescontinuous metering of caustic chemicals (e.g., lime, hydrated or sodaash) to raise the pH above 8 thereby increasing the rate of ironoxidation and precipitation as oxides (USEPA 1981). In addition tochemical additives, active treatment requires an assorted array ofpumps, aeration equipment and multiple oxidation and settling basins.Iron oxide solids produced in chemical treatment are low density (1 to4% solids) and highly contaminated with calcium, aluminum, manganese,and sodium deposits (Dempsey & Jeon 2001). The low-density solids slowlysettle in large open water basins, which require frequent and costlymaintenance to remove and dispose the accumulated solids.

Passive treatment systems rely on natural amelioration processes that donot require pumps or metered chemical additions. In general, minedrainage passes through open water ponds and/or aerobic wetlands whereabiotic and biotic processes contribute to the oxidation andprecipitation of iron (Hedin & Nairn 1993). Iron removal in passivetreatment systems require much larger land areas (10 to 20 timesgreater) than chemical treatment, which can become excessive for highflow and/or high iron concentration mine drainage discharges. Inaddition, iron removal in passive systems can be problematic withperformance varying with season, influent flow and concentration. Ironoxide solids produced by passive treatment systems have much highersludge density (15-30%) than chemical treatment and are frequently lesscontaminated (Dempsey & Jeon, 2001). Reported iron oxide content inpassive treatment solids varies from 50 to 90%.

AIS-treated waters produce a unique iron oxide sludge that (1) settlesat a rate faster than either chemically or passively produced solids;(2) is a high-density sludge with solids of approximately 30%; and (3)is a high-purity sludge with iron oxide content exceeding 95%. The priorart does not address the unique solids content of AIS-treated fluids.

Ferrous iron oxidation is usually the limiting step in the iron removalfrom iron-contaminated mine drainage. Iron oxidation has been describedto occur by two separate processes known as homogeneous oxidation, asolution oxidation process, and heterogeneous oxidation, asolid/solution interface oxidation process. Homogeneous oxidationinvolves soluble Fe²⁺, FeOH⁺, or Fe(OH)₂ ^(o) species in the presence ofdissolved oxygen (Stumm & Morgan 1996). This oxidation is stronglydependent on pH with slow oxidation occurring at pH 6 and rapidoxidation occurring above pH 8. Heterogeneous oxidation involves sorbedferrous iron on the surface of iron oxides in which the iron oxide actsas a catalyst (Dietz 2003 and Tamura & Nagayama 1976). At high ironoxide concentrations, heterogeneous oxidation has been found to produceoxidation rates greater than 100 times the rates observed in passivetreatment and comparable rates to chemical treatment (Dietz 2003, andDietz & Dempsey 2001). ). Heterogeneous ferrous iron oxidation (HeFIO)is described by the following model:$\frac{\partial\left\lbrack {{Fe}({II})} \right\rbrack}{\partial t} = {{- \left( {k_{{He}\quad 1} \times \lbrack{DO}\rbrack \times \frac{1 + \left( {\left\lbrack {{Fe}({II})}_{diss} \right\rbrack \times K_{1}^{app}} \right)}{\left\lbrack {\equiv {{Fe}({III})}} \right\rbrack \times \Gamma_{1} \times \left\{ H^{+} \right\}^{1}}} \right)} -}$$\left( {k_{{He}\quad 2} \times \lbrack{DO}\rbrack \times \frac{1 + \left( {\left\lbrack {{Fe}({II})}_{diss} \right\rbrack \times K_{2}^{app}} \right)}{\left\lbrack {\equiv {{Fe}({III})}} \right\rbrack \times \Gamma_{2} \times \left\{ H^{+} \right\}^{2}}} \right)$${pK}_{x,{T\quad 2}}^{app} = {{pK}_{x,{T\quad 1}}^{app} - \left( {\frac{{\Delta H}_{{rxn},x}^{0}}{2.303 \times R} \times \frac{T_{2} - T_{1}}{T_{2} \times T_{1}}} \right)}$${pk}_{{Hex},{T\quad 2}} = {{pk}_{{Hex},{T\quad 1}} - \left( {\frac{E_{a,x}}{2.303 \times R} \times \frac{T_{2} - T_{1}}{T_{2} \times T_{1}}} \right)}$Summary of parameters and constants in the ferrous iron sorptionheterogeneous ferrous iron oxidation (HetOX) models. Sub- Sub- ModelModel Model Parameter Description (x = 1) (x = 2) [Fe(II)] Ferrous IronConcentration, molar varies Varies ∂[Fe(II)]/∂t Ferrous Iron OxidationRate varies varies [DO] Dissolved Oxygen Concentration, varies variesmolar [Fe(II)]_(diss) Dissolved Fraction of Ferrous Iron, varies variesmolar [≡Fe(III)] Suspended AIS as Ferric Iron varies variesConcentration, g/L {H⁺} Hydrogen Ion Activity, molar varies varies {H⁺}= 10^(−pH) k_(Hex) (M⁻¹s⁻¹) Oxidation Rate Constant 0.105 38.0 E_(a,x)(kJ/mol) Activation Energy of Oxidation 60.7 60.7 Reaction K_(x) ^(app)(M^(x−1)) Surface Complexation Constant 10^(−1.265) 10^(−10.78) Γ_(x)(mol/mol) Sorption Site Density 0.0045 0.212 ΔH⁰ _(rxn,x) (kJ/mol)Enthalpy of Sorption Reaction 69.0 96.2 {H⁺} Hydrogen Ion Coefficient 12 Coefficient (x)Homogeneous oxidation is by far the dominant process in both chemicaland passive treatment, typically accounting for greater than 95% of theoxidation. This occurs because (1) chemical treatment occurs at high pHwere homogeneous oxidation is by far the fastest oxidation either withor without suspended iron oxide solids; and (2) passive treatment is anon-mechanical approach that does not allow for the suspension of highconcentrations of iron oxide (>200 mg/L) that would be needed to haveheterogeneous dominated ferrous iron oxidation.

Alkalinity may need to be generated to complete the precipitation ofoxidized ferrous iron where the source water alkalinity (mg/L as CaCO₃)to iron (mg/L as Fe) ratio is less 1.7. The low pH (approximately 5 to6) and/or high carbonic acid concentrations (P_(CO2) approximately 0.1to 0.5) found in many iron-contaminated waters (i.e., mine drainage)results in the rapid dissolution of carbonate minerals (such ascalcite), thereby producing alkalinity at concentrations higher thanwill typically occur in natural systems. A type of passive treatment,known as Anoxic Limestone Drains (ALD), has been found to producealkalinity greater than 300 mg/L (Hedin et al 1994). Other research hasfound carbonate dissolution occurs rapidly until pH greater than 6 isachieved and the rate of dissolution is directly proportional to thesurface area of the carbonate mineral present (Amrhein et al 1985;Pearson & McDonnell 1974). Testing done with a relatively unusedmaterial, pulverized limestone, in AIS treatment has been shown toadequately address the alkalinity issue due to rapid dissolution of thecarbonate in the high ferrous oxidation reaction rate environment of AISin combination with the complete mixing in the AIS reactor.

Therefore, it is the object of this invention to provide a treatmentprocesses and apparatus to oxidize and remove ferrous iron fromiron-contaminated mine waters at pH (less than 7) typically found iniron-contaminated waters.

Another object of this invention is to oxidize and remove ferrous ironfrom iron-contaminated waters by using the higher oxidation ratessupported by heterogeneous oxidation and providing a source ofalkalinity where inadequate alkalinity is present to complete theoxidation and precipitation of iron.

It is also an object of this invention to develop a simple means ofcollecting and concentrating the iron oxides produced by theiron-contaminated liquid treatment processes and apparatuses.

Other objects will be readily apparent after reading the description andreviewing the figures described below.

SUMMARY OF INVENTION

The invention involves an apparatus consisting of a single tank ormultiple tank assembly (in series or parallel) containing aerationand/or mixing apparatus, storage capacity for activated iron solids(AIS), a method of concentrating iron oxides in the reactor, time and/orflow-based process controls, and a waste activated iron solids (WAIS)apparatus. The invention also includes apparatus to add alkalinematerial (such as, pulverized calcite limestone) directly to thecontainer assembly where additional alkalinity is needed to complete theferrous iron oxidation and precipitation reactions and a separatecontainer assembly to thicken iron oxides produced by the treatmentprocess. The invention has the capacity to discharge substantially ironfree water with circumneutral pH.

The following description will provide a complete understanding of theinvention when reviewed in connection with the accompanying drawingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a preferred treatment system foroxidizing and removing ferrous iron from a flow of iron-contaminatedmine water.

FIG. 2 is a schematic cross-sectional view of a preferred embodiment ofthe AIS container assembly.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a plan view of the treatment system. An iron-contaminatedwater source (1) is directed into a least one AIS container assembly (4)or more preferably a plurality of AIS container assemblies. The means ofdirecting the iron-contaminated water into at least one AIS containerassembly may be by gravitational force or by pumping theiron-contaminated liquid into the AIS container assembly. When aplurality of AIS container assemblies are used in the treatment ofiron-contaminated water, a means for collecting and distributing theiron-contaminated water, such as a header system or distribution tankassembly, precedes the AIS/container assembly (3).

The source of iron-contaminated fluid is directed through a firstconduit (2) that is engaged with the inlet of the AIS container assembly(4) or a plurality of AIS container assemblies. Each AIS containerassembly in a plurality of AIS container assemblies is identical asshown in FIGS. 2 a and 2 b, a cross-section view of the AIS containerassembly. FIG. 2 a is a sequencing batch reactor (SBR) containerassembly where all processes (fill, react, flocculation, settling, AISretention, decant, and AIS wasting) occur sequentially within one (1)container assembly. FIG. 2 b is a flow-through container assembly having(1) at least two completely stirred reactors (CSTR) in series; (2) anupflow reactive bed clarifier following the CSTR; and (3) a system inthe upflow reactive bed clarifier to re-circulate and waste AIS. Thecontainer assembly method includes:

A system of the present invention has the following features:

-   -   1) A means for directing the fluid to be treated into a        container assembly having the features described herein;    -   2) A means of aeration and mixing within the container assembly        to provide sufficient oxygen for ferrous iron oxidation, carbon        dioxide removal for optimal pH operation, and suspension of the        activated iron solids (AIS) in solution;    -   3) A means of storing or re-circulating AIS within the container        assembly to maintain sufficiently high reactor iron oxide        concentrations to catalyze ferrous iron oxidation;    -   4) A means of decanting or overflow from the container assembly        to remove treated iron-contaminated fluid;    -   5) A means to remove excess iron oxides from the container        assembly; and    -   6) A means of controlling the duration of the various container        assembly processes such as fill, reaction, flocculation,        settling and decant. Such means include may include any of the        commercially available means (e.g., the Tork adjustable cycle        timer, the Tyco Time Delay Relays, the Ametek National Controls        Corporation Multi-range Delay on Break or the Grasslin        Timemaster GMX Series 24 hr 7 day cycle timer).

The method of the present invention includes the following steps:

-   -   1) Directing a fluid to be treated into a container assembly        having the features described herein;    -   2) Aerating and mixing iron-contaminated fluid within a        container assembly to provide sufficient oxygen for ferrous iron        oxidation, carbon dioxide removal, and suspension of the        activated iron solids (AIS) in solution;    -   3) Storing or re-circulating AIS within the container assembly        to maintain sufficiently high reactor iron oxide concentrations        to catalyze ferrous iron oxidation;    -   4) Decanting the container assembly to remove treated        iron-contaminated fluid;    -   5) Removing excess iron oxides from the container assembly; and    -   6) Controlling the duration of the various container assembly        processes such as fill, reaction, flocculation, settling and        decant to optimize the process and desired output        characteristics. Commercially available timers and controls are        described above.

The method may also include a plurality of container assemblies operatedwith an inlet header and a means for selectively isolating the flow toselected container assemblies. Processing steps in the AIS/SBR Containerassembly are described below:

Fill Step. Iron-contaminated fluid enters at least one AIS/SBR tankassembly. Preferably, for an efficient process, the tank is filled tocapacity with such iron-contaminated fluid. In some preferredembodiments the iron-contaminated fluid is mixed, aerated or both duringthe fill step. The temporal duration of the fill step may vary dependingon fluid flow rate and characteristics, tank volume and the chemistry ofthe iron-contaminated fluid. Commercially available floats and relayswitches may be used in this step.

Alkaline Addition Optional Step. Alkaline material optionally may beadded to an AIS/SBR tank assembly after or during the fill steppreferably using a doser assembly (5 on FIG. 1). The amount of alkalinematerial added to the iron-contaminated fluid in the AIS/SBR tankassembly may vary depending on the chemistry of the iron-contaminatedfluid and the amount of alkalinity needed to complete ironprecipitation. A commercially available timer and control may be used inthis step.

React Step. Oxidation and precipitation occurs in an AIS/SBR tankassembly during the react step. In addition, in cases in which alkalinematerial is added, the dissolution of the material and the generation ofalkalinity occur in conjunction with the oxidation and precipitation ofiron. Iron oxides retained in the AIS/SBR Tank Assembly are suspended influid providing a surface for heterogeneous ferrous iron oxidation. Ironoxides in suspension during the react step for mine drainage typicallyrange from approximately 500 up to 5,000 mg/L as iron and depend on thechemistry of the iron-contaminated fluid and the mixed fluid in theAIS/SBR tank assembly during the react step. Precipitation of ferriciron produced from the oxidation of ferrous iron is rapid and requiresmuch less time than the ferrous iron oxidation. React durations willvary depending on iron-contaminated fluid ferrous iron concentration,the volume of iron-contaminated fluid to be treated, pH, dissolvedoxygen and alkalinity. When the iron-contaminated fluid is mine drainageand standard AIS/SBR tank assemblies are used, the duration of the reactperiod is generally less than two hours.

Flocculation Optional Step. AIS and new iron oxides formed during thereact step may benefit from an optional flocculation step to createlarger iron oxide particles that settle more readily and easily. Theoptional flocculation step involves slow mixing to provide a fluidvelocity in the reactor equal to or less than 0.001 ft/sec in an AIS/SBRtank assembly to enable iron oxide particle interaction andagglomeration. Flocculation durations vary depending on the desiredoutput and characteristics of the fluid and particles after the reactstep. When treating iron-contaminated mine drainage in standard AIS/SBRtank assemblies, this step may last as long as one-half hour induration. A commercially available timer and control may be used in thisstep.

Settle Step. Iron oxides are removed from suspension in the AIS/SBR tankassembly by substantially ceasing and mixing or aeration treatment ofthe iron-contaminated fluid. The substantially quiescent conditions inthe AIS/SBR Tank Assembly permit AIS and newly formed iron oxides tosettle and accumulate in the bottom of an AIS/SBR tank assembly. Settlestep durations vary depending on the AIS concentration in the AIS/SBRtank assembly and desired purity of the resulting fluid. When treatingiron-contaminated mine drainage in standard AIS/SBR assemblies, thisstep generally is less than two hours in duration. A commerciallyavailable timer and control may be used in this step.

Decant Step. Subsequent to the settle step, treated fluid in an AIS/SBRtank assembly is removed from the tank assembly during the decant step.The decant step involves the removal, preferably rapid removal, ofsubstantially clarified supernatant fluid that overlies fluid containingsettled AIS. Typically, less than 75% of the fluid in the tank isdecanted although both the volume and time of the decant step will varydepending on the desired characteristics of the decanted fluid, thevolume of the tank and the rapidity and thoroughness of the settlingstep. In a preferred embodiment for treating iron-contaminated water,the decant period to remove 75% of the volume of the fluid in the tankwherein the tank is a standard volume, the mine drainage has standardcharacteristics, the time for the decant step generally is less thanone-half hour and is determined based on a per cent of tank drawdown.Commercially available floats and relay switches may be used in thisstep.

AIS Wasting Step. Excess AIS that results from newly formed iron oxides,periodically are removed from the AIS/SBR tank assembly in a step knownas AIS wasting. AIS wasting may occur during any of the above steps andoptionally can be conducted during a plurality of steps. The duration,volume of AIS removed, purity of AIS removed and frequency of this stepwill vary depending on the characteristics of the iron contaminatedfluid to be treated, the application and duration of the other steps,the use of optional steps, and the desired characteristics of effluent.A commercially available timer and control may be used in this step.

Steps in the process using two-stage flow-through AIS container assemblycomprise:

-   -   1) Inflow step. Iron-contaminated fluidenters the AIS container        assembly, preferably on a continuous basis.    -   2) Alkaline addition optional step. Alkaline material optionally        is added to the first reactor in the two-stage flow-through AIS        container assembly, preferably on a continuous basis (5 on FIG.        1). The amount of alkaline material applied varies depending on        the characteristics of the chemistry of the iron-contaminated        fluid and the amount of alkalinity needed to complete the iron        precipitation.    -   3) Oxidation and precipitation Step. Oxidation and precipitation        occurs in the first and second reactors (Stage 1 and Stage 2).        Iron oxides re-circulated to the first reactor are suspended        through aeration and mixing to provide a surface for the        heterogeneous ferrous iron oxidation. This high iron oxide        concentration preferably is maintained by flow-through in the        second reactor. Iron oxides in suspension in the first and        second reactors may be in the range from approximately 500 up to        3,000 mg/L as iron depending on the chemistry of the        iron-contaminated fluid and the mixed fluid in the first and        second reactors. Precipitation of ferric iron produced from the        oxidation of ferrous iron is rapid and requires much less time        than the ferrous iron oxidation. First reactor and second        reactor volumes and detention times vary depending on        iron-contaminated fluid flow, ferrous iron concentration, pH,        dissolved oxygen and alkalinity, but usually comprises less than        two hours of detention time.    -   4) Solids removal Step. AIS and new iron oxides formed in the        first and second reactors are removed and collected in the        upflow reactive bed clarifier. The hydraulic design of the        system allows for a suspended layer of highly concentrated iron        oxides, ranging from 10,000 to 60,000 mg/L and functions as a        filter separating particulate iron oxides from the flow from the        second reactor. The highly concentrated layer of iron oxide        continues the oxidation and precipitation of iron and can be        employed as a stand-alone unit. The size of the upflow reactive        bed clarifier depends on the flow and chemical characteristics        of the water being treated, but is approximately in the range of        1,500 to 4,000 gallons per day for every square foot of upflow        reactive bed clarifier surface area.    -   5) AIS recirculation and wasting Step. AIS collected in the        upflow reactive bed clarifier is continuously removed and        re-circulated to the first reactor using a solids or air lift        pump system, or a combination thereof Excess AIS, a result of        newly formed iron oxides, are periodically or continuously        removed from the container assembly using this recirculation        system, but diverting the AIS to a holding tank or thickener.

In an embodiment of the present invention that employs this method andsystem, the AIS container assembly or plurality of AIS Containerassemblies is connected to an outlet conduit (6 on FIG. 1) into whichtreated fluid is discharged from the AIS container assembly. The outletdischarges optionally into a receiving waterbody or an additionaltreatment system. Decant fluid or effluent from the AIS Containerassembly will have pH greater than 6 and iron concentrations of 5 mg/Lor less depending on the effluent criteria or treatment goals.

The method and system according to the present invention optionallyincludes an additional method of and system for thickening iron oxidesproduced by the foregoing method and system. An iron oxide thickeningsystem comprises:

-   -   1) A means of conveying fluids containing iron oxides to a        container;    -   2) A container in which fluids containing iron oxides are        retained to provide additional settling time, slow mixing of the        fluid to increase solids, or both;    -   3) A means of removing concentrated iron oxide solids from the        container; and    -   4) A means of decanting supernatant substantially free of iron        solids from the container.

Iron oxide thickening steps of the method of the present inventioninclude:

-   -   1) Conveying fluids containing iron oxides to a container;    -   2) Retaining a fluid containing iron oxides in a container for        sufficient time for iron oxides to concentrate in the fluid by        removal of water accomplished by providing additional settling        time, slow mixing of the fluid containing iron oxide to increase        the removal of water, or to both settle and mix such fluids;    -   3) Removing concentrated iron oxide solids from the container;        and    -   4) Decanting a supernatant substantially free of iron solids        from the container.

In an embodiment of the present invention that employs this method andsystem, waste activated iron solids (WAIS), the excess AIS produced byan iron oxidation treatment method or system according to the presentinvention, is directed into a container. Such fluid can be directed intothe container by using a variety of means including pumps, gravitationalforce, a combination of both, or other means. See step 7 on FIG. 1. Thecontainer and thickening step decreases the fluid content of the ironoxide solids and thereby increases the solid content of the iron oxidesolids. The iron oxide thickener container system consists of acontainer assembly containing a supernatant decant pump and a solidrecovery pump. The container assembly may also provide a means formixing the fluid to aid in removing excess water from the iron oxidesolids. Iron oxides resulting from such a step and system typically havea solid content up to 40%. Solids recovered from such processes andsystems have commercial reuse potential.

It will be understood from the above description that the presentinvention is related to a new device and treatment process foriron-contaminated water, such as mine drainage. This process and devicemay decrease the treatment area or volume or construction costs comparedto passive treatment approaches; and decrease treatment costs comparedto conventional chemical treatment through the elimination of the use ofcostly chemicals (e.g., lime and polymers) or their replacement withlower cost chemicals (e.g. pulverized limestone). The process may proveto be an economical alternative to both current passive treatment andchemical treatment approaches. The process has the added benefit ofproducing a relatively pure and easier to recover iron oxide solid thatmay have commercial value.

Although preferred embodiments of the invention have been described indetail herein, it will be appreciated by those skilled in the art thatvarious modifications and alternatives to the preferred embodiments maybe developed in light of the overall teaching of the disclosure.Accordingly, the particular arrangements are illustrative only and arenot limiting as to the scope of the invention, which is to be given fullbreadth of the amended claims and any and all equivalents thereof

1. A system for removing ferrous iron from a fluid comprising: a. Atleast one first container for receiving iron-contaminated fluid whereinsaid first container has at least one means of ingress and egress offluid; b. A means of transporting iron-contaminated fluid into saidfirst container; c. A means of aerating and mixing iron-contaminatedfluid within said first container; d. A means of decanting substantiallyiron-free supernatant fluid from said first container without disturbingsettled iron oxides; and e. A means of controlling the volume andtemporal duration of transporting fluids in and out of said firstcontainer, aerating and mixing a fluid within said first container, andmaintaining a fluid in a quiescent state in said first container.
 2. Asystem according to claim 1 having a plurality of first containers.
 3. Asystem according to claim 2 further comprising a means for selectivelydirecting the flow of a fluid to at least one of said first containers.4. A system of claim 1, 2 or 3 further comprising a means for deliveringalkaline-bearing material into said first container.
 5. A system ofclaim 1, 2, or 3 further comprising: a. A means for conveying fluid froma first container into a second container; b. A means of mixing fluidsin said second container; c. A means of removing iron oxides from saidsecond container; and d. A means of decanting a substantially iron-freesupernatant fluid from said second container.
 6. A system of claim 4further comprising: a. A means for conveying fluid from a firstcontainer into a second container; b. A means of mixing fluids in saidsecond container; c. A means of removing iron oxides from said secondcontainer; and d. A means of decanting a substantially iron-freesupernatant fluid from said second container.
 7. A method of removingferrous iron from a fluid comprising: a. Filling at least one firstcontainer with an iron-containing fluid; b. Aerating the fluid within afirst container sufficiently to ensure ferrous iron oxidation; c. Mixingfluid within the first container sufficiently to maintain a suspensionof iron oxide solids necessary to catalyze ferrous iron oxidation; d.Storing activated iron solids within a first container sufficiently tomaintain high reactor iron oxide concentrations necessary to catalyzeferrous iron oxidation; e. Decanting a substantially iron-freesupernatant fluid from a first container; and f. Removing excess ironoxides from a first container.
 8. A method according to claim 7 whereina plurality of first containers are filled with a fluid to be treated.9. A method according to claim 8 further wherein fluid is selectivelydirected either simultaneously or sequentially into first containers fortreatment.
 10. A method of claim 7, 8 or 9 further comprising addingalkaline-bearing material into a first container in sufficient quantityto provide sufficient alkalinity to precipitate iron oxides in a fluidto be treated.
 11. A method of claims 7, 8, or 9 further comprising: a.Conveying fluid from a first container into a second container; b.Mixing fluids in a second container; c. Removing iron oxides from asecond container; and d. Decanting a substantially iron-free supernatantfluid from a second container.
 12. A method of claim 10 furthercomprising: a. Conveying fluid from a first container into a secondcontainer; b. Mixing fluids in a second container; c. Removing ironoxides from a second container d. Decanting a substantially iron-freesupernatant fluid from a second container.
 13. A method of claim 7, 8 or9 further comprising mixing fluids sufficiently to promote flocculationafter said storing of activated iron solids within a first containersufficiently to maintain high reactor iron oxide concentrationsnecessary to catalyze ferrous iron oxidation.